Spinel-structured LixMn2O4 (x = 1.0, 1.02, 1.04, and 1.06) cathode materials have been synthesized by a solidstate method using Mn3O4 and Li2CO3 as raw materials. The Mn4+ content gradually decreases from 84.80% to 82.62% and then increases from 82.62% to 88.98%, when the Li content increases from 1.00 to 1.06. The rate capability of the LiMn2O4 samples evidently increases as the lithium content increases from 1.00 to 1.06. Electrochemical impedance spectroscopy results indicate that the R-sf values gradually increase from 58.33 Q to 133.1 Omega and then decrease from 133.1 Omega to 68.79 Omega when the Li concentration increases from 1.00 to 1.06. The 114 values also increase from 25.67 Omega to 37.84 Omega and then decrease from 37.84 Omega to 16.69 Omega, when the Li concentration increases from 1.00 to 1.06. These changes in Mn4+ content, R-sf, and R-ct with the increase in Li content are related to changes in the second phase in LiMn2O4.